Board & Card Games Stack Exchange is a question and answer site for people who like playing board games, designing board games or modifying the rules of existing board games. It's 100% free, no registration required.

In Rex: Final Days of an Empire, it is possible for the following sequence of events to occur:

Sol Offensive is revealed as the Influence card and affects a zone occupied by the Sol player's troops (allowing him to move said to anywhere on the board).

The Sol player places some number of troops in a space occupied by another player (e.g. Letnev, but it is irrelevant).

The Sol Offensive is completed otherwise, and a second Influence card is revealed as a Temporary Cease Fire.

The Sol player and the Letnev player (who would otherwise have battled) now form an alliance.

Now, the placement of the Sol player's troops is illegal (the rules state you cannot place troops in a space occupied by an ally's troops). According to the rules (or an official ruling or FAQ), what should be done?

Heh, I don't know this game but I'm very amused by this complex game state and the discussions it is generating on the internet. I take it you're aware of this thread: fantasyflightgames.com/…?
–
thesunneversetsApr 3 '12 at 11:08

I actually hadn't seen it, no, but the option (mentioned therein) we've been using previously was "If the two players ally, then the Sol player must immediately move that army again, as though the Sol Offensive card had just come up." It's just a house rule, though.
–
Ian PugsleyApr 3 '12 at 13:03

@thesunneversets You might have heard of the original. It's quite famous as a great game for cutthroat screw-jobs.
–
Alex PJul 13 '12 at 12:35

Apparently there are not yet any errata to clarify this issue, but a couple of house rule options leap to mind:

Your house rule seems like a good one. Since it must follow a Sol Offensive, re-moving the Sol units (i.e. changing the move that had just been made) seems to result in the fewest extra changes to the game

You could disallow alliances between players that occupy the same space. This might be a little harsh, but it's by far the easiest to enforce, and since the Sol player was attacking anyway, they won't be too often worried about being refused this option!

The suggestion I'd be tempted to make if it came up in a game I was playing (which it hasn't) is that the alliance is allowed, on the requirement that the pieces don't still occupy the same space during the battle phase (i.e. one of the players must move during their movement). You could require that agreeing this is a requirement of forming an alliance. If neither player moves, then the alliance is void because offensive troops were not removed from an ally's area (which works thematically too). Since players only get one move, forming this alliance would cost one of them a fair part of their turn, which might be too high a cost to form the alliance, but as long as the parties are aware of this I don't think this is a problem.